No particular ethnic group or wine-producing country has a higher or lower alcohol content in its wine. The alcohol content in wine varies from product to product all over the world, based on grape harvest conditions and winemaking techniques or style desired.

As foodie says, your boss's generalization is definitely wrong. However, Italy probably does make more 6% to 8% alcohol wines (such as Asti Spumante and various table wines made from the Moscato grape) than any other major wine growing country -- which may have lead to the misunderstanding.